Sound attenuating gas conduit



Nov. 12, 1963 E. LUDLow ETAL 3,110,358I

SOUND ATTENUATING c-As coNDuIT Filed July 10, 1961 2 Sheets-Sheet l.IMPJT v/ S E. LUDLOW ETAL v SOUND ATTENUATING GAS CONDUIT Nov. 12, 19632 Sheets-Sheet 2 Filed July l0, 1961 INVENTORS. fom/N0 awww mwBYf/VJAM//v In w/N masia' i H TTOB NEPS.

United States Patent O 3,110,353 SUND AT'EENUATWG GAS CGNDUIT EdmundLudlow and Beniamin H. lrwin, Columbus, lud., assignors to ArvinIndustries, Inc., Columbus, Ind., a corporation of indiana- Filed .'lulylil, 1961, Ser. No. 122,891 Claims. (Cl. 181-59) This invention relatesto a sound attenuating gas conduit, and more particularly to a conduitfor conveying, and attenuating the noise level of, a gas stream.

It is the object of our invention'to provide a sound attenuating gasconduit which can Ibe simply and easily manufactured from inexpensivetubing, which will hav'e its weight ldistributed along its length, andwhich can be tuned to attenuate different and overlapping bands of soundwave frequencies.

It -is a specific object of our invention to provide a sound attenuatinggas conduit which can be used in association `with an internalcombustion engine for conveying, and attenua-ting the noise level of,the exhaust .gases emanating from said engine.

In accordance with one form of our invention, there is provided anclon-gated pipe forming a gas-flow passage and having a plurality ofinterlitting shells mounted within it. Each of said shells is providedwith a closed end which is received in the open end of the next adjacentshell with portions of the walls of the intertitting ends of each pairof said shells being disposed in spaced relation to each other so thatthe interiitting ends of each pair of shells dene a resonator throat.Said throat is in open communication with the gas-dow passage and aresonator volume formed by the adjacent closed ends of said pair ofshells and the side walls of the shell in said pair off shells in whichthe other'shell in said Vpair is received. In this manner, each pair ofinterlitting shells defines a resonator throat and volume disposed inthe gas-flow passage for attenuatin'g the noise level of the gases 4insaid passage.

Other objects and features of our invention will become apparent fromthe more ydetailed description which follows and'from the accompanyingdrawings, in which:

FIG. .l is a fragmentary longitudinal section of a sound attenuating gasconduit embodying our invention;v

FlG. 2 is a vertical section taken on the line 2 2 of FIGA;

FIG. 3 is an enlarged isometric view of the resonatorforming shell shownin FIG. l;

FIG. 4 is an isometric view o-f another embodiment of theresonator-forming shell shown in FIG. 3;

FlG. 5 is ya fragmentary longitudinal section of a sound attenuatinglgas conduit employing another embodiment of our resonator-formingshell;

FlG. 6 is a fragmentary longitudinal section of a sound attenuating gasconduit employing another embodiment of our resonatornforming shell; and

FiG. 7 is afragrnentary longitudinal section of a sound attenuating gasyconduit employing another embodiment of our resonator-forming shell.

Our invention is adapted to convey a moving gas stream cfrom one pointto another andto attenuate the noise level of said gas stream. Althoughit may be ernployed to convey, and attenuate the noise level of, manydifferent ykinds of gas streams, it is primarily adapted for use with aninternal combustion engine in an automotive vehicle .for conveying, andattenuating the noise level of, the exhaust gases discharged from saidengine. The sound waves in such exhaust gases extend over a wide rangeof frequencies, i.e., from about 30 cycles per second to about 1,500icycles per second. Our invention is adapted to attenuate the noiselevel of such a range of dd M5358 Patented Nov. 12 1953 ICC frequencies,and is particularly well adatped to attenuate the difficult to silencefrequencies below 200 cycles per second. Our conduit may be used alone,lin which case it extends `directly yfrom the exhaust manifold of anengine to the desired Igas discharge point, or it may be used incombination with other sound attenuating systems or components, in whichcase it may constitute one or more short sound attenuating conduitsemployed with said systems.

As shofwn in FIG. 1, our invention comprises an elongated pipe 1tlforming a gas-flow passa-gc. Said pipe may be in the form of a runitarycontinuous length of pipe or a series of interconnected pipe sections.Mounted within said pipe is a plurality of elongated, axially aligned,resonator-forming shells 12 conveniently 'formed from lengths ofmetal-tubing. Each of the shells 12 comprises a body 14 open at one ofits ends and integral and continuous `with a neck 16 at its oppositeend. The end of the neck 16- remote from the body 14 is closed as at 18.

As shown in FIGS. l and 2, the neck 16 of each of the shells 12 has aslightly smaller cross-section than the body 14 to permit each pair ofsaid shells to be intert one `within the other, as will be more fullyexplained hereafter.

The body 14 is provided with one or more deformations adjacent the openend thereof. Such deformations in the embodiment shown in FIG. 3ycomprise axially extending inwardly projecting beads 20, formed in theshell side walls and spaced about its circumference, with the innerfaces of said beads defining the locus of a circle having -a diameterapproximating the outer diameter of the neck 16.

ln assemblying our shells 12, the neck 16 of one of said shells is slid,desirably as a press lit, into the open end of the Ibody 14- of the nextadjacent shell. rThe beads 2li hold the portions of the side Wa-lls ofthe intertitting ends of said shells disposed between said beads inspaced relation to each other so that said wall portions define laresonator throat indicated at 22 in FIG. 2. The closed ends 18 of teachpair of interlitting shells form the end walls of a resonator volumeindicated at 2Liin FIG. 1, with the side walls of said volume beingformed by the side walls of the shell in which the next adjacent shellneck 16 is inserted.

As will lbe apparent, the size of each of the volumes 249 yand lthelength of each of the throats will be determined by the length to whichone shell is inserted within the other. As will be understood from knownprinciples of acoustics, the length and cross-sectional area of thethroats 22 and the size of the volumes 24 determine the' sound wavefrequencies which 4the resonators formed by said volumes and throatswill attenuate. l-f the throats have relatively long lengths and/ orrelatively large crosssections, the :resonators will attenuaterelatively low sound wave frequencies. Conversely, resonators havingshorter throats and/or smaller cross-sections will attenuate the highersound wave frequencies. formed by the intertitting shells 12 may betuned to attenuate `different and overlapping bands of sound Wavefrequencies by controlling the length to which said shells are insertedone within the other, and/ or controlling the cross-sectional extent ofthe beads Ztl'.

The press tit provided by the beads 2l) will retain the shells in theldesired position of intertitting adjustment during :assembly prior tomounting said shells in the pipe 1l). With the several shells disposedin such ian intertitting engagement said shells may be rigidly securedto the inner Wall lof the pipe 10 such las Iby welding or the like todispose the resonators formed by said shells in direct acoustic andthermal coupling with the gases in said pipe to attenuate the noiselevel of the sound waves in said gases.

Thus, the resonators Another embodiment of our shell construction isi-llustrated in FIG. 4, and comprises a shell 25 having a body 26 open`at one of its ends and having its opposite end integral and continuouswith a smaller diameter neck 27. The end of the neck 27 opposite thebody 26 is closed as at 3), .and said neck is provided with outwardlyprojecting beads 3l `forme-d in its side walls. rlhe outer faces of thebeads 3l define the locus of a circle having a diameter approximatingthe inner diameter of the body 26. In this manner, `a plurality yof theshells 25 may be inserted one within the other in a press t to define aseries of resonators. The beads El hold portions of the side walls ofthe neck 27 of one shell 25 and body 26 of the next adjacent shell inwhich said neck is inserted in spaced relation to form a resonatorthroat in open communication with the gas stream and a resonator volumeformed by the adjacent end `vvalls 30 of the intertting pair of shellsand the side walls of the shell in which said neck is inserted. With theshells 25 disposed in the -desired interiitting relationship, they maybe mounted in the gas-How passage of a gascarrying pipe in the samemanner as the shells 12.

Another embodiment of our shell construction is illustrated in FIG. inwhich a plurality of interitting shells 35 yare secured to the innerwall of a pipe 36 dening a gas-flow passage. Each of the shells 35 has abody 37 open at one of its ends and having its opposite end integral andcontinuous with a smaller .diameter neck 38 having its end opposite saidbody 37 closed las at 39. The neck 36 has an outer diameterapproximating the inner diameter of the lbody 37 so that the shells maybe press lit in interiiting relationship to ydefine a series ofresonators. One or more outwardly projecting beads 40 are formed in theside walls of the body 37' of each shell so that with the next adjacentshell neck 38 disposed in the open end of said body, Isaid beads and theunderlying portions of the side walls of said neck define one or moreresonator throats 4l in open communication with the interior of the pipe36 and a resonator volume 42 fonmed by the adjacent end walls 39 of theinteriitting pair of shells land the side walls of the shell in whichthe next adjacent shell is inserted.

FIG. 6 illustrates still another embodiment of our shell construction inWhich a plurality of intertJtin-g shells 44 are secured to the innerwall of a pipe 45 dening a gasilow passage. Each of the shells 44 has abody 46 open at one of its ends and having its opposite end integral andcontinuous with a smaller diameter neck 48 having its end opposite saidbody 46 closed as lat 50. The -neck 48 has an outer diameterapproximating the inner diameter of the body 46 so that 4the shells maybe press t in interiitting relationship to deiine a series ofresonators. One or more inwardly projecting beads 51 are formed in theside walls of the neck 48 ot each shell so th-at with said neck insertedin the body 46 of the next adjacent shell, said beads 5l and theoverlying portions of the side walls of said body will definel one ormore resonator throats 52 in open communication with the interior of thepipe 45 and a resonator volume 54 formed by the adjacent end Walls Si)of the interitting pair of shells and the side Walls of the shell inwhich the next adjacent shell is inserted.

Although `all of the beads formed in the shells shown in FIGS. 1 6 havebeen illustrated as rectilinear, axially extending beads, such beads mayhave any desired configuration. It is only essential that said bead-s beformed in the shells in positions such that they form open endedthroats-open to both the gas-how passage and the resonator volumes.

A sound attenuating conduit employing still another embodiment of ourshell construction is illustrated in FIG. 7. As shown, a plurality ofinteriitting shells 55 are secured to the inner wall of a pipe 56defining a gas-flow passage. Each oct said shells comprises a body 58open at one of its ends and having its opposite end integral andcontinuous with a smaller diameter neck 60 having its end opposite saidbody closed as at 62. 'Ihe neck 60 has a smallerouter diameter than theinner diameter of the body 58 and is received in the body 58 of the nextadjacent shell to dispose the side walls 'of the intertting shell endsin spaced relation to define a resonator throat 63. Said throat is inopen communication with .the interior of the pipe 56 and a resonatorvolume 64 yfor-med by the adjacent end Walls 62 of the interitting pairof shells and the side walls of the shell in which the next adjacentshell is inserted.

The -throats of the 4resonators formed by the shells shown in FEGS. l-6are tuned by adjusting the cross-sectional extent Aof the beads :and thelength to which each pair of shells are interfit. In the embodimentyshown in FG. 7, such tuning is controlled by the length to which ieachpair of shells are intert Iand by -the relative diameters of the shellnecks and bodies. As the diameters of the necks 66 become progressivelysmaller th-an the diameters of the Abodies 58, the side Walls of saidnecks and bodies are spaced farther apart when the shells are interiit,and the resonators attenuate progressively lower sound w-avefrequencies.

While we have described the modifications of our resonator-formingshells as having a circular cross-section and being adapted to besecured directly to the inner Wall of an elongated pipe, it is to beunderstood that such shells may have any desired cross-sectionalconfiguration and may be mounted within a gas-carrying pipe in anyconvenient manner.

We claim as our invention:

l. In a sound attenuating gas conduit, an elongated pipe forming agas-How passage having unrestricted flow at its ends, and a plurality ofaxially disposed interitting shells carried within said passage, each ofsaid shells having a closed end received in an open end of the nextadjacent shell, iirst portions of the side walls of interitting ends ofeach pair of shells being interit against each other and second portionsof the side walls of said interiitting ends disposed in spaced relationto deiine a resonator throat in open communication with said gas-flowpassage and a resonator volume formed by the adjacent closed ends ofsaid pair of shells and the side walls ofthe shell in said pair ofshells in which the other shell in said pair is received, whereby saidresonator throat and volume will attenuate the noise level of the gasesin said gas-How passage.

2. In a sound attenuating gas conduit, an elongated pipe forming agas-How passage having unrestricted flow at its ends, and a plurality ofaxially extending interiitting shells carried Within said passage, eachof said shells having a closed end received in the open end of the nextadjacent shell and abutting the inner face of the side walls thereof,one or more elongated projections on the side walls of at least one ofthe shells in each pair of interitting shells operatively associatedwith the side walls of the other shell in said pair of shells to disposeportions of the side Walls of the interitting ends of each pair ofshells in spaced relation to denne a resonator throat in opencommunication with said gas-iiow passage and a resonator volume formedby the adjacent closed ends of said pair of shells and the side Walls ofthe shell in said pair of shells in which the other shell in said pairis received, whereby said resonator throat and volume will attenuate thenoise level of the gases in said gas-How passage, the length to whichone shell in said pair of shells is received in the other shell in saidpair of shells being adjustable to adjust the spacing between theirclosed ends and the length of the interfit of their ends to control thesize and length of said resonator volume and throat.

3. In a sound attenuating gas conduit, an elongated pipe forming agas-flow passage having unrestricted flow at its ends, and a pluralityof interfitting elongated shells carried within said passage, each ofsaid shells having one of its ends closed and its opposite end open, theclosed end of said shell having a smaller cross-section than the openshell end whereby each shell is receivable in the open end the nextadjacent shell, rst portions of the side walls of the intertting ends ofeach pair of shells presst together and second portions of the sideWalls of said interfitting ends being disposed in spaced relation todene a resonator throat in open communication with said gas-flow passageand a resonator volume formed by the adjacent closed ends of said pairof shells and the side walls of the shell in said pair of shells inwhich the other shell in said pair is received, whereby said resonatorthroat and volume will attenuate the noise level of the gases in saidgas-How passage.

4. The invention as set forth in claim 3 with the addition that each ofsaid shells has one or more inwardly extending projections formed in itsside walls adjacent its open end and engageable with the side walls ofthe next adjacent shell received in said open end to form said rstportions and to dispose said second portions of said pair of shellsbetween said first portions in spaced throatforming relation.

6 5. The invention as set forth in clairn 3 with the addition that eachof said shells has one or more outwardly extending projections formed inits side Walls adjacent its closed end and engageable with the sidewalls of the next adjacent shell in which said closed end is received toform said rst portions and to dispose said second portions of said pairof shells between said rst portions in spaced throat-forming relation.

References Cited in the le of this patent UNITED STATES PATENTS2,099,858 MacKenzie et al Nov. 23, 1937 2,109,995 Hawle Mar. 1, 19382,176,615 Starkweather et al. Oct. 17, 1939 FOREIGN PATENTS 484,771Great Britain May 10, 1938 980,535 France Dec. 27, 1950

1. IN A SOUND ATTENUATING GAS CONDUIT, AN ELONGATED PIPE FORMING AGAS-FLOW PASSAGE HAVING UNRESTRICTED FLOW AT ITS ENDS, AND A PLURALITYOF AXIALLY DISPOSED INTERFITTING SHELLS CARRIED WITHIN SAID PASSAGE,EACH OF SAID SHELLS HAVING A CLOSED END RECEIVED IN AN OPEN END OF THENEXT ADJACENT SHELL, FIRST PORTIONS OF THE SIDE WALLS OF INTERFITTINGENDS OF EACH PAIR OF SHELLS BEING INTERFIT AGAINST EACH OTHER AND SECONDPORTIONS OF THE SIDE WALLS OF SAID INTERFITTING ENDS DISPOSED IN SPACEDRELATION TO DEFINE A RES-